The present invention relates generally to a process for the agglomeration of solid peroxides which rapidly decompose upon melting and to solid peroxide agglomerates made by this process.
Solid, organic peroxides are often obtained in the form of a lumpy, dusty powder having unacceptable flow characteristics which makes the handling and particularly the dosing of such peroxides extremely difficult. For example, when the peroxides contain too many fines they present difficult handling problems. In addition, the tendency of some peroxides to cake hampers their ability to dissolve in the reaction medium thereby significantly slowing commercial cross-linking processes. Accordingly, there is a need in the art to agglomerate solid organic peroxides to improve their flow properties, eliminate excess fines, provide a product with a narrow particle size distribution and to improve the dissolution time of such peroxides in reaction media.
A process for agglomerating solid peroxides is known from Japanese patent application JP 51-096783 published on Aug. 25, 1976. In this process, organic peroxide is melted and dispersed in a liquid medium in the presence of a high polymer surfactant and the dispersion liquid is then cooled to solidify the organic peroxide. While this process is satisfactory for some peroxides, it cannot be used for peroxides which rapidly decompose when heated to their melting points. Thus, this process is limited to peroxides which have melting points that are substantially lower than their decomposition temperatures.
Another process for agglomerating solid peroxides is known from Research Disclosure May 10, 1980, no. 193002, wherein it is taught to prepare peroxide granules by mixing a solid peroxide with a dispersing medium, heating the peroxide-containing medium to a temperature above the melting point of the peroxide and rapidly cooling the mixture. Again, this process is limited to peroxides which have melting points that are substantially below their decomposition temperatures since the process requires the melting of the peroxide.
U.S. Pat. No. 4,818,425 is representative of several publications which disclose processes for coating peroxyacids to be used in solid bleaching compositions. The coating is accomplished by agglomerating the peroxyacid in an aqueous suspension in the presence of a water-impermeable material which melts at a temperature substantially below the decomposition temperature of the peracid. In the agglomeration process, the aqueous suspension is agitated while being heated to a temperature above the melting point of the waterimpermeable material, and subsequently cooled to solidify the coated agglomerates of the peroxyacid. The purpose of this coating process is to prevent the occurrence of the phenomena termed pin point spotting when these peracids are employed as solid bleaching agents in textile laundering applications.
Finally, Japanese patent application JP 54-029882 published on Mar. 6, 1979 discloses a desensitized solid organic peroxide composition and a method for its preparation. In the method, a solid peroxide which is explosive to shock is wetted with water and added to additional water to produce an aqueous suspension. Up to 20 wt % of a second peroxide, which is nonexplosive, is dissolved in an organic solvent such as acetone and the solution of the second peroxide is mixed at room temperature with the suspension of the first peroxide and vigorously mixed to obtain a mixed solution containing a solid agglomerate which is subsequently separated and dried. While this process safely produces a desensitized agglomerate of the explosive peroxide, the resultant agglomerate exhibits an unacceptably wide particle size distribution and poor flow properties which make it difficult to handle.
The present invention has as its object to overcome the drawbacks of the prior art agglomeration processes listed above. Surprisingly, it has been found that the agglomeration process of the present invention provides an excellent method for providing solid organic peroxides which decompose upon melting in a form which is easier to handle and use than the presently available forms of these peroxides. More particularly, the present invention provides solid peroxides with a narrow particle size distribution, less fines, better flow properties, and, in some cases, better solubility in reaction media. All of these advantages are achieved while at the same time providing a safe agglomeration process and without introducing foreign materials into the product which significantly impair their efficacy for their intended use.